The present invention relates to a semiconductor device, and more particularly, to a semiconductor device having a plurality of operation modes selectable by an external device.
A semiconductor device may include a chip incorporating an internal circuit having a plurality of selectable operation modes. Such a chip has external terminals for receiving setting signals corresponding to the operation modes from an external device. However, it is difficult to provide setting signals for a large number of operation modes if the number of external terminals is limited. Therefore, it is desirable that setting signals corresponding to a plurality of operation modes be provided to an internal circuit through a single terminal.
In one method for providing operation mode setting signals to the internal circuit of a chip from an external device, a setting signal of a predetermined voltage level is provided to a mode setting external terminal.
In this method, two different operation modes may be set by one external terminal if the setting signal has two different voltage levels, namely, an H level and L level. In this case, if the setting of a larger number of operation modes is necessary, the number of external terminals for receiving setting signals needs to be increased.
In order to enable many types of operation mode setting signals to be provided without increasing the number of terminals, an external terminal capable of receiving setting signals of many different voltage levels may be used, while incorporating a voltage detector circuit in the internal circuit.
Japanese Laid-Open Patent Publication No. 7-263505 describes an operation mode detector for determining an operation mode by detecting current flowing through a pad. This operation mode detector detects a plurality of operation modes with a common pad.
Japanese Laid-Open Patent Publication No. 5-190771 describes the connection of an external circuit to an output terminal to drop the voltage of an internal circuit and switch functions of the internal circuit based on the change in the voltage.